Azeotropic distillation of isopropyl alcohol from diisopropylamine



Patented June 20, 1050 AZDOI'BOP'IO DIS'I'ILM'I'ION 0F rsornom AIOOHOLI'BOH nnsornomnmna Everet For Smith. 'lerre M Ind Solvents lndaeorporationof adgnorto corporatm'terrellaute, Maryland NDra F 25.1

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13 Claims. (Cl. 2010-42) This invention relates to a method forseparating diieopropyiamine from mixtures comprising diisopropyiamineand isopropyl alcohol.

In the production of dilsopropylamine by reacting lsopropyl alcohol withammonia, for example.orbyhydrogenatingamlxtureofisopropyiamine andacetone, the product always contains an appreciable proportion ofisopropyl alcohol. Separation of the diisopr wlamine from the isopropylalcohol cannot be accomplished by direct fractional distillation, owingto the small diflerence between the boiling points of the two compounds(83.7 and 524 0., respectively). Moreover, I have discovered that theprior-art process of distilling the mixture with water to separate thediisopropynmine-water aneotrope boiling at 74.2 C. does not eifect acomplete separation of the mine from the alcohol. but gives instead adistillate consisting ordinarlly of 83% dlisopropylamlne. 12% water, and5% isopropyl alcohol. Even when the distillatlon is carried out in thelaboratory under very carefully controlled conditions. I have found thatthe diisopropylamine-water aaeotrope contains around 1% of isopl' wlalcohol.

I have now discovered a superior process for isolating diisopropylamine,in which isopropyl alcohol is removed completely from mixturescontaining diisopropylamine and isopropyl alcohol by anazeotropic-dlstillation method comprising the following steps: Water andan inert organic liquid of a type subsequently to be described are addedto the mixture of diisopropylamlne and isopropyl alcohol: aheterogeneous ascotrope boiling substantially below thedinopropylamine-water aaeotrope and containing isopropyl alcohol in bothof the phases is fractionally distilled; the distillate phases areseparated: one phase is refluxed to the still column,

while the other phase is withdrawn until all of the isopropyl alcoholhas been removed from the still; the remaining water and inert organicliquid are separated; and the diisopropylamine is subsequently distilledin substantially pure form.

It will be readllyapparent to those skilled in the art that inmy processthe treatment of the mixture of diisopropyiainine and isopropyl alcoholcan be continued, additional'water and inert organic liquid beingintroduced into the still if necessary. until tests on the materialremaining "in the still kettle show that it is entirely free fromisopropyl alcohol. The prior-art process.

on the other hand. attempts the much more dlflicult operation ofdistilling a material directly away from an impurity. In the prior-artproc- 2 ess. the quality of the dual product is therefore lesssusceptible to control, since it is directly dependent on the sine andtype of still column. the distillation rate, and the reflux ratio, andmaybegreatlyaifected byanirregularityinthe operation of the process.

In one specific embodiment, my invention comprises the following steps:

1. To a mixture containing diisopropylamine and isopropyl alcohol areadded water and an inert organic liquid capable of forming aheterogeneous aneotrope with water and isopropyl alcohol boilingsubstantially below the diisopropylamine-water azeotrope (74.2 C.)

2. The mixture is distilled through an efllcient fractionating column,and a heterogeneous aaeotrope comprising isopropyl alcohol, water, theinart organic liquid. and a small iproportion of diisopropylamine iscondensed overhead.

3. The distillate layers are separated. the upper layer comprising theinert organic liquid is refluxed to the still column, and simultaneouslythe lower layer comprising water and hopropyl alcohol is withdrawn untilall of the isopropyl alcohol has been removed from the still.

4. The distillation is continued, additional water being added to thestill if necessary. and the aqueous layer of the distillate is refluxedto the still column while the upper layer comprising the inert organicliquid is withdrawn until the vapor temperature at the top of the stillcolumn reaches 74' 0., at which point all of the aiitzienr't organicliquid has been removed from the 5. The water remaining in the still isremoved.

6. Finally, the diisopropylamine is fractionally distilled insubstantially pure form.

In the foregoing embodiment of my invention, the inert organic liquid isadded to the still charge in a quantity suiilcient to produce theheterogeneous azeotrope of isopropyl alcohol. water. and the inertorganic liquid. Ordinarily. a quantity of the inert organic liquid equalto from about 5 to 15% of the weight of diisomopylamine in the stillcharge will be found sullcient. However, the quantity will vary.depending on the size of the fractionating column, and especially on theamount of liquid held up in the decanter.

The quantity of water present in the still charge in the foregoingembodiment of my invention will also vary, depending on the quantity ofisopropyl alcohol present in the still and on the identity of the inertorganic liquid. It is essential that a suillcient quantity of water headdedtothestill either initiallyorpriortothe completion of Step 3,described above, to carry away all of the isopropyl alcohol presentinitially in the still charge. The required quantity of water willtherefore be a function of the weight of lsopropyl alcohol in the stillcharge and of the concentration of isopropyl alcohol in the aqueouslayer of the isopropyl alcohol-waterinert organic liquid azeotrope. Whenbenzene is used as the inert organic liquid, for example, theconcentration of isopropyl alcohol in the water layer averagesapproximately 8%; with cyclohexane as the inert organic liquid, theproportion of isopropyl alcohol averages about 15%; with n-hexane, 15%:and with isopropyl ether, An excess of water is preferably added to thestill charge to insure the complete removal of the isopropyl alcohol.When benzene is used as the inert organic liquid, the ratio of water toisopropyl alcohol in the original still charge is therefore preferablyat least about 8:1 by weight.

In Step 5, the removal of the water remaining in the still may becarried out as described in the prior art by treatment of the stillresidue with a dehydrating agent such as sodium hydroxide. I havediscovered, however, that in the complete absence of isopropyl alcohol,the diisopropylamlne-water azeotrope is heterogeneous at temperatures inexcess of 27 C. I have therefore found it convenient to remove theresidual water from the still residue by fraotionally distilling thedilsopropylamine-water azeotrope to a decanter maintained at atemperature above 2'! C., refluxing the upper (diisopropylamine) layer,simultaneously withdrawing the lower (aqueous) layer until thedistillate becomes homogeneous, and subsequently removing the smallquantity of water remaining in the still as an intermediate tractionboiling from '74 to around 82 C.

To those skilled in the art, it will be obvious that the variousfractions separated from the still during Steps 2 to 5, inclusive, inthe foregoing description of my invention may be reprocessed or recycledconveniently. The aqueous isopropyl alcohol layer from Step 1 may befractionally distilled to separate the isopropyl alcohol. The migture ofinert organic liquid and a small proportion of diisopropylamine fromStep 4 may be recycled in batches. The water separated from the still inStep 5 and the succeeding wet diisopropylamine intermediatefractionmayalsoberecycledin succeedingbatches.

In a second specific embodiment, my invention comprises the followingsteps:

1. To a mixture containing diisoprqpylamine and isopropyl alcohol areadded water and an mm organic liquid capable of turnin a heterogeneousaseotrope with water and isopropyl alcohol boiling substantially belowthe diisopropylamine-water aseotrope (74.2 (7.).

2. Themixtureisdistilledthroughaneflicient fractionating column, and aheterogeneous assotrope comprising isopropyl alcohol, water, theinertorganicliquidandasmallpropcrtionof diisopropylamine is condensedoverhead.

8. The dktillate layers are separated, the aqueous layer is refluxed tothe still column, and simultaneously the layer comprising isopropylllcoholandtheinertorganicllquidiswithdrawn until all of the isopropylalcohol and the inert organicliquid have beenremoved fromthestill.

4. Thewaterremaininginthestillisremoved.

I. Finally, the diisopropylamine is fractionally distilled insubstantially pure form.

g thebasisoftherelativeofisopmpyl alcohol between the organic andaqueous layers ofthedlstillateandonthebasisoftherela'tive economics ofthe two procedures.

lnorderforthefosegoingmethodstobeeilw tive, the inert organic liquidmust have the following properties and all manic liquid having thedesignated group of properties are suitable for use in my 1. It must beunreactive with water. isopropyl alcohol, and diisopropyhniine at up toaround C.

2. Itmustformaaseotropewith water boiling sumciently below the boilingpoint of the diisop pylamine-water (74.2 C.) to permit satisfactoryseparation by tractional distillation.

3.Theinertorganicliquidoriiswaterareotropemusthaveaboilingpointsuflieientlybelow diisopropylamine to permit easyby fractional distillation.

Numerous inert organic liquids satisfy the foregoing requirementsregarding boiling point and azeotrope-formation. Bpeclally suitable area number of ethers and branchedchain, and cyclic hydrocarbons. Asspecific examples of the above classes of inert organic liquids suitablefor use in my room may be cited the following: eyciohexane, nhexane,22-dimethylpentane, 2,2,3-irimethylbutane. l-hexene, z-hexene.it-hexene, isopropyl ether, butyl methyl ether. ethyl isobutyl ether,butyraidehyde, and ethyl methyl hetone. Esters are definitelyunsatisfactory, owim to the fact that they react rapidly with lamine toform N-substituted amides.

Thevarious distillationstemmaybecarried out in conventional equipment,such as a still comprising a kettle. a column having phtes andbubble-caps in sufllelent number to separatefractionsboilingwithini-o'qofeabhothena condenser, a decanter arrangedto permit reflux of either upper or lower layer to the still column,andoneormorereeeiversofsuitabledesign.Theprocessmaybecarriedoutstepwiseinbatchtype apparatus, or it may becarried out continuouslyin aseriesofsflllcolumnaeachcohnnnservingtocarryoutonestepoftheprocess.

The following examples are given to illustratemyinventiomandarenottobeas limitingittothe exactmatei'lmsmorconditionsdescribed:

Example 1 To a batch of crude diisopropylaminecomprisingiliopartsbyweightotflflmopylamine been removed iron: the stillcharge. Pii'ty parts of distilled water were then added to the still,

and the distillation was resumed with total reflux oi the water layer.The upper layer. containing benzene and diisopropylamine, was taken oilup to a vapor temperature of 74 6.. at which temperature all oi thebenzene had been removed. The mixture oi benzene and diisopropylaminewas recycled in subsequent batches. At 74' C. the distillate, consistingof the diisopropylamine-water aseotrope, was heated in a decanter to atemperature above 27 C. to cause separation into layers, the upper layerwas refluxed to the still column, and the lower (water) layer waswithdrawn until the distillate became homogeneous. Subsequently. a smallwet-diisopropylamine fraction, boiling range Ii-82 0., was taken oil andheld for recycling. Finally the pure diisopropylamine traction, boilingaround 84' C. was distilled. A total of 256.8 parts of diisopropylaminewas separated, analyzing 99.6% pure.

Example 2 To a batch of crude diisopropylamine comprising 400 parts byweight of diisopropylamine and 26.1 parts of isopropyl alcohol in astill kettle were added 244 parts of water and 86.9 parts ofcyclohexane, and the mixture was distilled through an eiilcientfractionating column. The vapors were condensed and allowed to pass intoa decanter, from which the upper (cyclohexane) layer was totallyrefluxed to the still column. and the lower (aqueous) layer comprising15% isopropyl alcohol and 0.7% diisopropylamine was taken oil until thedistillate became homogeneous, at which point all oi the isopropylalcohol had been removed from the still charge. To the still were thenadded 50 parts oi water (free from isopropyl alcohol), and thedistillation was resumed with total reflux oi the water layer. The upperlayer, containing cyclohexane and diisopropylamine, was taken oil up toa vapor temperature of 14 C., at which temperature all of thecyclohexane had been removed. The mixture of cyclohexane anddiisopropylamine was recycled in subsequent distlllations. At 14 C. thedistillate, consisting oi the diisopropylaminewater azeotrope. washeated in a decanter to a temperature above 27 C. to cause separationinto layers, the upper layer was refluxed to the still column, and thelower (water) layer was withdrawn until the distillate becamehomogeneous. Subsequently, a small wet-diisopropylamine iraction,boiling range ii-82 C., was taken oil and held for recycling. Finally,the pure diisopropylamine traction, boiling around 84 0., was distilled.A total of 290 part: or diisopropylamine was separated. analyzing 00.6%pure.

Emmple 3 To a batch oi crude diisopr i ylamine comprising 400 parts byweight of diisopropylamine and 26.1 parts oi isopropyl alcohol in astill kettle were added 244 parts oi water and 33.0 parts oi an edlcientn-actionating "column. The vapors were condensed and allowed to new intoa dc;- canter. from which the upper (n-hexane) layer was totallyrefluxed to the still column, and the lower (aqueous) layer comprising15% isopropyl alcohol and 0.04% diisopr pylamine was taken oil untilthedistillate became homogeneous, at which point all of the isopropylalcohol had been removed from the still charge. To the still were thenadded 50 parts 0! water (tree from isoprml alcohol), and thedistillation was completed as in Example 1. A total or 206 parts ordiisopropylamine was separated, analyzing 90.2% pure.

Example 4 To a batch'oi crude dilsopropylaminc compris ing 400 parts-oiweight of diisopropylamin and 26.! parts of isopropyl alcohol in a stillkettle were added 244 parts or water and 33.0 parts of isopropyl ether,and the mixture was distilled through an efllcient tractionating column.The vapors werecondensed and allowed to flow into a decanter. from whichthe upper (isopropyl ether) layer was totally refluxed to the stillcolumn, and the lower (aqueous) layer comprising 5% isopropyl alcoholand 0.03% dlisopropylamine was taken ofl until the distillate becamehomogeneous, at which point all of the isopropyl alcohol had beenremoved from the still charge. The distillation was ompleted asdescribed in Example 1. A total oi 256 parts oi diisopropylaminewasseparated, analyzing 99.8% pure.

Example 5 To a batch oi crude diisopropylamine comprising 400 parts byweight oi diisopropylamine and 26.2 parts 01' isopropyl alcohol in astill kettle were added 56.0 parts of water and 105 parts of benzene,and the mixture was distilled through an eilicient iractionating column.The vapors were condensed and allowed to flow into a decanter, fromwhich the lower (aqueous) layer was otaily refluxed to the still column,and the upper (benzene) layer comprising an average or 80% benzene, 15%isopropyl alcohol, and 5% diisopropy was taken oil until the temperatureat the top oi the column had reached 74 C., at which: point all of theisopropyl alcohol and benzene had been removed from the still charge.At'li' C. the distillate, consisting of the diisopropylaminewaterazeotrope, was heated in a decanter to a temperature above 27' C. tocause separation intolayers, the upper layer was refluxed, and the lower(aqueous) layer was withdrawn until the the amine, removing the residualwater and.

hydrocarbon. and tractionally distilling the diisopropylamine.

2. The process of claim 1 wherein said hydron-hexane, and the mixturewas distilled through 1. carbon is benzene.

3. The process oi claim 1 wherein said hydrocarbon is cyclohexane.

4. m of claim 1 in which the hydrocarbon is bennene, and in which theratio of henacne in isopropyl alcohol in the original charge is at leastabout 4:1 by weight.

5. A of separating dlisopropylamine from mixtures containingdiisopropylamlne and isopropyl alcohol which comprises adding to such amixture water and an organic liquid having the characteristic propertiesof being nonreactive with water, isopropyl alcohol and dlisopropylamineat temperatures up to 80C., of forming a heterogeneous aseotrope withwater boiling sufiiciently below the diisopropylamine-water aseotrope toermit separation by fractional distillatlon. the boiling point ofdiisopropylamlne being sumciently above the boiling point of acomposition selected from a class consisting of said organlc liquid andthe water aaeotrope thereof to permit separation of said compositionfrom mixtures thereof with diisopropylamine by tractional distillation,then azeotropically distilling the resulting miximre to separate thelsopropyl alcohol and the organic liquid from the amine, removing theresidual water and iractionally distilling the diisopropylamine.

6. The process of claim 5 wherein said inert organic liquid is analiphatic ether.

7. The process of claim 6 wherein said inert organic liquid is ispropylether. 1

8. The process of claim 5 in which the residual inert organic liquid isremoved by azeotropic distillation with water.

9. A process for separating diisopropylamine from mixtures containingdiisopropylamine and isopropyl alcohol which comprises adding to thesaid mixtures water and an inert organic liquid having thecharacteristic properties of beingnonreactive with water, isopropylalcohol and diisopropylamine at temperatures up to 80 0., of forming aheterogeneous azeotrope with water boiling sufliciently below thediisopropylaminewater azeotrope topermit separation by fractionaldistillation, the boiling point of diisopropylamine being sufllcientlyabove the boiling point of a composition selected'from a classcornisting of said organic liquid and the water azeotrope thereof topermit separation of said composition from mixtures thereof withdiisopropylamine by fractional distillation, then iractionallydistilling the mixture through an efllcient column, separating thedistillate layers in' a decanter, refluxing the layer comprising theinert organic liquid to the still column and simultaneously withdrawingthe layer comprising water and isopropyl alcohol, continuing thedistillation until all of the isopropyl alcohol has been removed,fractionally distilling the water azeotrope of the inert organic liquidto a decanter, separating the layers of the distillate, refluxing theaqueous layer, and simultaneously withdrawing the layer comprising theinert organic liquid until all of the inert organic liquid has beenremoved, separating the residual water from the material remaining inthe still kettle, and subsequently iractionally distilling thediisopropylamine in substantially pure state.

10. A process for separating diisopropylamine from mixtures containingdiisopropylamine and isopropyl alcohol which comprises adding to thesaid mixtures water and an inert organic liquid having thecharacteristic properties oi being nonreactive wlth water, isopropylalcohol and diisopropylamlne at temperatures up to 80C. of forming a,heterogeneous aseotrope with water boiling suiilclently below thediisopropylamine-watei' aaeotrope to permit separation by fractionaldistillation, the boiling point of diisopropylamine being suilicientlyabove the boiling point oi a composition selected from a classconsisting oi said organic liquid and the water aaeotrope thereof topermit separation or said composition from mixtures thereof withdiisopropylamlne by fractional distillation, then iractlonallydistilling the mixture through an eiflcient column separating thedistillate layers in a decanter, refluxirm the layer comprising theinert organic liquid to the still column and simultaneously withdrawingthe layer comprising water and isopropyl alcohol, continuing thedistillation until all of the isopropyl alcohol has been removed, addinga small proportion of water to the still, fractionally distilling to adecanter, separating the layers of the distillate, refluxirm the aqueouslayer and simultaneously withdrawing the layer comprising the inertorganic liquid until all of the inert organic liquid has been removed,continuing to distill to a decanter maintained at a temperature of notless than 2'7 0., separating the layers of the distillate, refluxing thelayer comprising diiscpropylamine and simultaneously withdrawing theaqueous layer until the distillate becomes homogeneous, removing theresidual water as a small intermediate fraction comprising mainlydiisopropylamine. and subsequently fractionally distilling thediisopropylamine in substantially pure state.

11. The process of claim 10 in which the ratio of water to isopropylalcohol in the orglnal still charge isat least about 8:1 by weight.

12. A process for separating diisopropylamine from mixtures containindilsopropylamine and isopropyl alcohol which comprise adding to the saidmixtures water and an inert organic liquid having the characteristicproperties of being nonreactive with water, isopropyl alcohol anddiisopropylamine at temperatures up to C., 01' forming a heterogeneousazeotrope with water boiling suillclently below thediisopropylamine-water azeotrope to permit separation by fractionaldistillation, the boiling point of diisopropylamine being sufllclentlyabove the boiling point of a composition selected from a classconsisting of said organic liquid and the water azeotrope thereof toermit separation of said composition from mixtures thereof withdiisopropylamine by tractional distillation, then fractionallydistilling the mixture through an eilicient column, separating thedistillate layers in a decanter, refluxing the aqueous layer to thestill column and simultaneously withdrawing the layer comprisingisopropyl alcohol and the inert organic liquid, continuing thedistillation until all of the isopropyl alcohol and the inert organicliquid have been removed, separating the residual water from thematerial remaining in the still kettle, and subsequently iractlonallydistilling the diisopropylamine in substantially pure state.

13. A process for separating diisopropylamine from mixtures containingdiisopropylamine and isopropyl alcohol which comprises adding to thesaid mixtures water and an inert organic liquid having thecharacteristic properties of being nonreactive with water, isopropylalcohol and diisopropylamine at temperatures up to 80" 0., of forming a.heterogeneous azeotrope with water boiling sufllciently below thediisopropylamine-water azeotrope to permit separation by fractionaldistillation, the boiling point of diisopropylamine 15 beingsuiliciently above the boiling point of a 9 composition selected from aclass consisting of said organic liquid and the water azeotrope thereofto permit separation of said composition from mixtures thereof withdiisopropylamine by tractional distillation, then iractionallydistilling the mixture through an eilicient column. separating thedistillate layers in a decanter, refluxing the aqueous layer to thestill column and simultaneously withdrawing the layer comprisingisopropyl alcohol and the inert organic liquid, continuing thedistillation until all oi the isopropyl alcohol and the inert organicliquid have been removed. continuing the distillation to a, decantermaintained at a temperature of not less than 27 0.. separating thelayers of the distillate, refluxing the layer comprisingdiisopropylamine and simultaneously withdrawing the aqueous layer until10 the distillate becomes homogeneous, removing the residual water as asmall intermediate fraction 5 amine in substantially pure state.

EVEREI FOY SMITH.

REFERENCES CITED The following references are oi record in the tile 01'this patent:

UNITED STATES PATEN'IS Number Name Date 2,348,683 McKenna May 9, 1944 is2,363,157 Stasse Nov 21, 1944 2,363,158 Stasse Nov. 21, 1944 2,363,159Stasse Nam-21, 1944

1. A PROCESS FOR SEPARATING DISOPROPYLAMINE FROM A MIXTURE CONTAININGDISOPROPLAMINE AND ISOPROPHYL ALCOHOL WHICH COMPRISES ADDING TO SAIDMIXTURE WATER AND A HYDROCARBON WHICH FORMS A HETEROGENEOUS AZEOTROPEWITH WATER AND ISOPROPYL ALCOHOL BOILING BELOW THE DISOPROPYLAME-WATERAZEOTROPE, AZEOTROPICALLY DISTILLING THE RESULTING MIXTURE TO SEPARATETHE ISOPROPHY ALCOHOL FROM THE AMINE, REMOVING THE RESIDUAL WATER ANDHYDROCARBON, AND FRACTIONALLY DISTILLING THE DISOPROPYLAMINE.